Vibrating conveyors are often used to transport solid materials in and along a conveyor trough which is either generally horizontal, inclined or declined with respect to the conveying direction. Conveying troughs are oscillated at certain frequencies with amplitudes and directions of motion which are known to cause the desired material conveyances. The solid materials can be transported over distances of from several feet to several hundred feet. Longer vibrating conveyors, for example, those over forty feet, most commonly incorporate resonant frequency spring systems and are powered by displacement input drive systems, for example, crank arm assemblies, operating at or near the spring system resonant frequencies. Conveyors so constructed are known as resonant frequency vibrating conveyors and operate with reduced operating stresses and energy requirements.
Many vibrating conveyor applications require the ability to change the conveying speed of the material conveyance during the operation of the conveyor. In vibrating conveyor applications such as metering solid material, parts sorting and parts inspection, it is often desired to vary the material conveying speed during the operation of the conveyor.
One method for varying the material speed of a resonant frequency vibrating conveyor during its operation is to adjust the frequency of trough oscillation. This method is greatly limited because of the undesirable vibrations and stresses imparted to the vibrating conveyor apparatus when operated at frequencies substantially different from its resonant frequency.
Another method for varying the material speed during operation of a resonant frequency vibrating conveyor is to change the direction of oscillating motion. This requires changes to the resonant frequency spring systems and the displacement input drive system. The configuration of these systems are very costly to alter on a vibrating conveyor without compromising the strength and reliability of the apparatus.
A further method for varying the material conveying speed during conveyor operation is to change the amplitude of trough displacement. Varying the displacement of a displacement drive system is known, for example, one such vibrating conveyor construction is described in U.S. Pat. No. 5,404,996. Two cranks are mounted on a base, and a first crank arm is driven by a constant speed motor. The cranks are interconnected by sheaves and belts so that the motor driven crank arm provides power to the second crank arm. The interconnecting belts also extend around a mechanical phase angle adjustment plate which functions to vary the belt lengths interconnecting the crank arms, thereby varying the rotational phase between the crank arms. The distal ends of the crank arms are interconnected together by a linkage assembly that is also connected to the conveying trough. Changing the rotational phase angle between the crank arms changes the amplitude of displacement imparted to the conveying trough. The above device has a first disadvantage of requiring a complex linkage assembly interconnecting the crank arms and the trough. The oscillating motion of the crank arms is transmitted across four link elements and six pivot joints. The large number of pivot joints which are subject to wear during operation adversely impacts the cost and reliability of the conveyor drive. A second disadvantage to the system is the relatively complex phase angle adjustment mechanism that also has six rotating elements which are subject to wear during conveyor operation. Therefore, there is a need to provide a conveyor drive system for varying the and speed of material being conveyed along the conveyor utilizing a simple, reliable system having a minimum number of parts that are subject to wear and replacement.